Tween is a small library to perform tweening in Go. It has a minimal interface, and it comes with several easing functions.

Tween usage

func main() {
	// tween from 0 to 1 in 3 seconds
	tw := tween.NewTween(0, 1, 3*time.Second, tween.Linear, false)

	// advance by 1.5 seconds
	tw.Update(time.Millisecond * 1500)

	// get tween value at 1.5 seconds
	fmt.Println(tw.Value) // 0.5

	// merge multiple tweens into a sequence
	sequence := tween.NewSequence(
		tween.NewTween(0, 100, 3*time.Second, tween.InCubic, false),
		tween.NewTween(100, 40, 2*time.Second, tween.OutCubic, false),
		tween.NewTween(4, 100, 20*time.Second, tween.InOutBounce, false),
	)

	// advance by 7.5 seconds
	sequence.Update(time.Millisecond * 7500)

	// get sequence value at 7.5 seconds
	fmt.Println(sequence.Value) // 5.3125
}

See examples folder for more examples.

Easing functions are functions that express how slow/fast the interpolation happens in tween.

The easing functions can be found in the ease package.

They can be divided into several families:

• linear is the simplest easing function, straight from one value to the other.
• quad, cubic, quart, quint, expo, sine and circle are all "smooth" curves that will make transitions look natural.
• The back family starts by moving the interpolation slightly "backwards" before moving it forward.
• The bounce family simulates the motion of an object bouncing.
• The elastic family simulates inertia in the easing, like an elastic gum.

Each family (except linear) has 4 variants:

• In starts slow, and accelerates at the end
• Out starts fast, and decelerates at the end
• InOut starts and ends slow, but it's fast in the middle
• OutIn starts and ends fast, but it's slow in the middle